BOISE -- Idaho State Department of Agriculture officials say their agency has trapped more than 2,000 invasive Japanese beetles in Boise's Warm Springs area in an effort to isolate the pest's distribution and keep it from spreading into surrounding neighborhoods and farms.

The state began monitoring nurseries, airports and other high-risk sites for the beetle in 1990, deploying 200-300 traps per year. Prior to last summer, ISDA occasionally found just a few "lone hitchhikers" on nursery stock from other states.

Late last summer, ISDA captured 56 beetles, mostly in the eastern Boise neighborhood. The agency reported another four bugs were discovered last summer near a Kootenai County nursery, and a single bug was found near a Bannock County nursery.

The beetles feed on plant foliage and roots and can be destructive to home gardens, lawns and crops. They're especially fond of irrigated crops and turf. They arrived in the U.S. in 1916, in a shipment of iris bulbs from Japan to a New Jersey nursery and have taken hold in several eastern states. Western infestations have thus far been eradicated.

Based on last season's detections, ISDA set out several canister traps, each containing a pheromone to lure in Japanese beetles, and has found the insects throughout an 8-block area of Warm Springs this season.

Lloyd Knight, administrator of ISDA's Division of Plant Industries, said the beetles were discovered too late last summer for insecticides to work effectively. The agency has contracted with a a commercial spray applicator this season, which recently began applying granular treatments to kill grubs in turf and foliar sprays to kill feeding adults.

Knight said ISDA has detected feeding damage on some residential gardens, but no impacts on commercial agriculture.

"If you do surveys and treatments, you can usually keep these things from spreading," Knight said. "If we do our job right, we'll find them before they do much damage and get them treated."

Orem, Utah, is in the home stretch of eradicating a similar Japanese beetle outbreak that threatened orchards located near a residential area. Utah state entomologist Clint Burfitt said it takes two life cycles without insect detections to consider a population eradicated. Burfitt said a proven trapping methodology, high mortality of larvae to common pesticides and the fact that the beetles produce a single generation of offspring per year make them relatively easy to eradicate.

At the end of their lives, female beetles tend to lay eggs under turf, where larvae feed on roots. The adults hatch and "skeletonize" leaves, feeding on more than 300 hosts.

Burfitt believes Idaho's eradication program should protect agricultural fields adjacent to residential areas and enable the state to avoid trade quarantines for certain crops and nursery plants.

Utah Department of Agriculture and Food spokesman Larry Lewis said the Orem infestation, discovered in 2006, covered 100 square blocks at its peak, and treatments reduced bug populations by about 95 percent per year. For two years, residents of the treatment area were asked to refrain from planting gardens and accept free produce from the state instead.